Not Applicable
Not Applicable
This invention relates to press brakes or metal bending machines, and in particular, to a control system for the metal bending machine.
Press brakes or metal bending machines have long been used to form bends, for example, in metal. The metal bending machines have a movable ram and a fixed bed. A punch is fixed to the upper beam (or ram) and a die is fixed to the lower beam (or ram). Typically, press brakes built in the United States are down-acting machines (i.e., the ram moves down). Up-acting machines (the ram moves up) are more typical in Europe, but are also available in the United States.
In a typical press operation, the ram is moved towards the bed to an approach point where the gap between the punch and die is as small as possible, but large enough to insert the material to be bent. The sheet metal (or material to be bent) is then inserted and positioned in the press brake. The press brake is then activated again to bend the sheet metal. Once the sheet metal is bent, the ram is opened and the bent sheet metal is removed from the press brake.
Several different devices have been provided to help reduce the possibility of injury to press brake operators. One system employs a light curtain. In this system, an emitter is positioned on one side of the press brake to pass a beam of light in front of the press brake. A receiver on the opposite side of the press brake receives the beam of light. When the light beam is interrupted, the press brake reverses and opens. This worked well to help reduce injuries to press brake operators. However, often the bending metal would pass in front of the light beam, and block the light beam, causing the press brake to open. One method of avoiding this was to design the control system so that if it detected something that was very thin or narrow, it would interpret this to be the sheet metal, and the safety control system would not be activated. However, in some instances, the sheet metal would bend out of plane (i.e., it would form an angle of other than 90xc2x0 with the vertical) and would trip the control system, causing the press brake to open, interrupting the bending operation.
To overcome this problem, other systems relied on the fact that once the approach point is reached, an operator""s hand or finger could not fit between the punch and die. In these systems, any perceived break in the light beam prior to the brake press reaching its approach point would cause the press brake to open. However, a perceived break in the light beam after the press brake was reactivated to bend the sheet metal would be ignored. This avoided the problem of tripping the control system when the sheet metal bends out of plane.
These systems also worked well. However, none of the systems known compensated for failure in the relays of the control system (such as the relay contacts becoming welded). In these circumstances, the safety control system may become inoperablexe2x80x94either the control system would continuously send a signal to open the press brake, or it would not send a signal when the light beam is interrupted. Additionally, a reliable way to reset the safety control system is required, to help ensure that the brake press is free of obstructions before a bending cycle is started.
A press brake machine has a movable ram, a fixed bed, a drive for moving the ram toward and away from the bed, and a control system which controls movement of the ram. The control system includes an emitter which emits a beam of light and a detector assembly which detects an interruption of the light beam. The detector assembly outputting a first signal when the light beam is detected and a second signal when the light beam is interrupted. In response to the output of the second signal, the drive moves the ram away from the bed to open the press brake.
The emitter and detector can be positioned on opposite (i.e., left and right) sides of the press brake. Alternatively, the emitter and detector can be positioned on the same (e.g., left) side of the press brake, with, for example, the emitter being in a front plane of the press brake and the detector assembly being in a back plane of the press brake. A mirror assembly is positioned on the other (right) side of the press brake and receives the light from the emitter and reflects it back to the detector. This second arrangement provides for front and back light beams which are spaced apart by a distance approximately equal to the width of the die, and will detect something being inserted between the punch and die, whether the obstruction comes from the front or back of the press brake.
The detector assembly includes a first sensor, a second sensor, and a beam splitter. The emitter is aligned with the beam splitter so that the light beam is directed at the beam splitter. The beam splitter and mirrors directs a portion of the light beam to the first sensor and a portion of the light beam to the second sensor. The sensors produce an output in response to the detection of an interruption of the light beam. The first and second sensors each include a relay, the relays having coils movable between a first (energized) state and a second (de-energized) state, and contacts switchable between an open position and a closed position in response to the state of the coils. The coils are switched from the first state to the second state in response to the sensor output produced when an interruption of the light beam is detected. Importantly, the detector assembly""s second signal is output when either or both of the sensors detect that the light beam is interrupted. To accomplish this xe2x80x9ceither/orxe2x80x9d condition, the contacts (preferably the normally open contacts) of the first and second relays are connected in series. Thus, the relays, when connected in series, create a redundancy which allows the detector assembly to function properly when the contacts of one of the relays are welded closed.
The beam splitter preferably includes a threaded shaft and a head on the end of the shaft. The head preferably is integral with the shaft and comprises a pair of polished surfaces defining a triangle in cross-section. Because the splitter is on a threaded shaft, the precise position of the splitter can be adjusted to account for variance in the position of the sensors, to better aim the light at the sensors.
The press brake is provided with a reset switch, the contacts of which are movable between an open position and a closed position. The reset switch contacts are closed when the ram is in its opened position. The reset switch is connected in series between the output of one of the sensors and the relay coils. Hence, the reset switch receives its voltage from the sensor. The relay coils are maintained in their first, energized, state when both the switch is closed and when the sensor detects the light beam. If the sensor from which the reset switch receives voltage detects an interruption of the light beam, the relay coils are not energized, and a new bending cycle cannot be started. Once the bending cycle has started, and the ram begins to move towards the actuation point, the reset switch is opened, allowing the coils to be switched between their energized and de-energized states based solely on the output of the sensors.
The press brake is also provided with a muting switch which mutes the output of the sensors when the ram is being moved from the actuation point to the bed to bend sheet material placed in said press brake. The muting switch is in electrical communication with the relay coils and is closed when said ram reaches the actuation point and remains closed while the ram is moved from the actuation point to the bed. When the muting switch is closed, the coils are maintained in their first, energized, state such that the detector assembly outputs only the first signal, regardless of the output of the sensors. Thus, if the light beam should be interrupted, for example by the bending metal, the bending cycle will not be affected.